A gas detector tube for determining the quantity of oil mist in a gas sample has become known from DE 32 23 742 C2. A certain test gas volume is first drawn by means of a pump through the gas detector tube and the oil mist present in the test gas is deposited on a filter within the gas detector tube. An ampule containing sulfuric acid is then pierced, as a result of which the oil in the filter is dissolved and rinsed into a display layer via a distributor layer. A color display, which is proportional to the quantity of the oil mist filtered out of the test gas, is formed in the display layer.
The drawback of the prior-art gas detector tube is that a color chart is needed for the evaluation of the display in order to make it possible to state the quantity of oil mist. Such a color comparison is not always unambiguous and also depends on the user's individual color perception.